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C O U R S E 
Human Evolution: Past and Future
John Hawks, University of Wisconsin
C O U R S E   L E C T U R E 
Hominin Species and Speciation
Notes taken on March 26, 2017 by Edward Tanguay
why are species bounded from each other
we would expect to find
gradual changes in the fossil record
gradual gradations among living organisms, i.e. a continuous range of species of animals
as gradual changes occurred, they became more and more adapted to smaller habitats
those gradations gave rise to large populations and smaller populations
more populous species would continually replace the smaller ones
in Darwin's day, the fossil record was not very complete
today we have extraordinary records of some lineages
from Australopithecus anamensis
to Australopithecus afarensis
two species that lived between 4.2 and 2.9 million years ago
across much of East Africa
we see in them a record of gradual change
in Darwin's time, species were simply what naturalists said they were
they understood the morphological variation, i.e. study of the size and shape of anatomical features
Darwin's book: The Descent of Man, and Selection in Relation to Sex
concerned with the topic of whether different kinds of humans should be called different species or not
"It is a hopeless endeavor to decide this point until some definition of the term species is generally accepted. We might as well attempt without any definition to decide whether certain number of houses should be called a village, town, or city. We have a practical illustration of the difficulty in the never-ending doubts of whether many closely allied birds, mammals, insects, and plants which represent each other respectively in North America and Europe should be ranked as species or geographical races."
when paleoanthropologists name species in much the same way today, just in more sophisticated terms
the evidence that we use to decide whether members of a species have a close relationship is not often evidence that is closely at hand
the biological species concept
a species is a population that includes all of the populations that can actually or potentially reproduce with each other in their natural habitat
this definition focuses on reproduction
it doesn't matter in principle how different the members of these species look
as long as they are reproducing with each other in their natural habitats, in their natural populations
exist in at least four sub-populations across equatorial Africa
their close relatives the bonobos separated from the chimpanzees more than a million years ago
chimpanzee subspecies have existed for more than a half-million years
there is not much evidence that early hominim populations were comparable in their differences to one another as we see with chimpanzees and bonobos
but the difference between sub-species and species can be seen as arbitrary and depends on one's intentions
many conservation biologies who are concerned about protecting chimpanzees want to emphasize the biological differences between the different groups and would prefer that different sub-species be called different species
many biologies who are studying the fossil record who are trying to understand how various fossil forms are morphologically different and might be related to each other, are not ready to test how different those morphological differences are consistent with populations who are exchanging significant amounts of genes
Australopithecus afarensis is a descendant of Australopithecus anamensis
why don't we just call them one species?
we don't know that Australopithecus afarensis is the only decendent of Australopithecus anamensis
we later have more evidence of various hominim groups adapting to different kinds of ecologies
but until there is more information, paleontologists prefer to give groups names so they can communicate about them clearly
but we often don't have enough information to know when and where major changes might have arisen
the name gives paleontologists a way to deal with variation and to approach the hypotheses
when it is argued whether a species is valid or not, it is being argued whether one can trace the fossil record with the evidence that is available, or whether addition discoveries need to be made to find the common ancestors of these groups